Silver has been known as a purifying agent since ancient Egypt when it was employed to purify water for lengthy storage. Modern medicine makes use of silver as an antibacterial agent in the treatment of burns and eye infections in new-born babies (M. Potenza, G. Levinsons, AIM Magazine 59:39 (2004)). Silver solutions have been used as antibacterial agents in the treatment of infected wounds, and silver is used in the purification of water on the NASA space shuttle. The anti-inflammatory properties of silver have been shown by a reduced reddening of infected wounds edges. Other heavy metals, such as zinc, lead, gold, nickel, cadmium, copper and mercury, are also known to have anti-bacterial properties, but some of them cannot be used because of their toxicity or high costs. Among heavy metals, only silver, zinc and copper can be used as antibacterial agents. Zinc is the least effective of these, while copper, though highly effective against some mildews, and has a synergistic effect when combined with silver, cannot be used in contact with food. Silver ion is the most effective ion with the lowest toxicity. On this subject, see: J. M. Schierholz, L. J. Lucas, A. Rump, G. Pulverer, Journal of Hospital Infection (1008) 40: 257-262; Gadd G M, Laurence O S, Briscoe P A, Trevors J T. Silver accumulation in Pseudomonas stutzeri AG 259. Bio Metals 1989; 2: 168-173; Wahlberg J E. Percutaneous toxicity of metal compounds. Arch Environ Health 1989; 11: 201-203; Williams R L, Williams D F. Albumin adsorption on metal substrates. Biomat 1988; 9: 206.
Materials coated with silver release silver ions that attach to bacterial cells, incapacitating them and preventing them from growing or reproducing. As this process depletes silver from the material, a silver-based antibacterial product cannot be active indefinitely. When released by the material, silver ions act on the bacteria (see Y. Noue, Y. Kanzaki, Journal of Inorganic Biochemistry 67:377 (1997)), according to a still unknown mechanism, which can be summarized in this way: uptake of silver by a bacterial cell, leads to destruction of its cell wall, inhibition of reproduction and inhibition of metabolism (M. Potenza, G. Levinsons, AIM Magazine 59:39 (2004)). Silver has no toxic effects on living human cells. It has very potent antibacterial activity, since a solution with only 1 ppm of pure elemental silver has an effective bacterial killing action. Natural or synthetic materials (e.g., fabric, woven and similar), with antibacterial properties have already been realized in several fields, such as clothing, medicine, filtering systems, transportation and others. They have different shapes and tradenames but all of them are very expensive, because of the existing difficulties in their realization.